1. Field of the Invention
This invention relates to an improvement in water-cooled panels for use in arc furnaces, particularly for steel making to avoid the production of hot-spots.
2. Description of the Prior Art
Recently, in arc furnaces, particularly large arc furnaces for use in steel works, it has been proposed that an electric power 1.5 to 2 or more times as much is fed to the furnaces for the purpose of facilitating temperature raising operation after melting so as to effectively shorten refining time as well as for the purpose of shortening melting time so as to increase productivity. However, it has been found that the supply of such a large electric power to the arc furnaces leads to an increase in the number of melting-lost portions as produced due to arc heat in a local area of the furnace wall close to its electrode and called "hot-spot."
Among measures therefor it has been proposed to provide an arc furnace with a water-cooled panel having a smooth surface at an area of the furnace wall which is so close to its electrode that hot-spots intend to be produced therein, whereby the furnace wall is prevented from being locally melted and lost. In this proposed arrangement, since the water-cooled panel is located behind the furnace wall made of refractory material such as refractory bricks, some of the refractory bricks covering the box have intended to be subject to hot-spot and be melted and lost. In addition to this, since the refractory bricks covering the panel is heated at its outer surface by arc heat and is cooled at its inner surface by the cooling effect of the panel, there have occurred distortions due to the difference between thermal expansions at the outer and inner surfaces, resulting in "spalling" to the extent that the outer surface of the panel is exposed to the inside of the furnace. Therefore, since the outer exposed surface of the panel is subject directly to arc heat, it has been necessary to increase the flow of water coolant circulating through the panel in order to prevent overheating of the panel surface. As a result, the thermal efficiency of the furnace has been lowered. Although slugs have been scattered to and deposited on the exposed surface of the water-cooled panel to form a layer of deposited slug which would play the same role as that of the covering refractory bricks mentioned above, the layer of deposited slug has been so thin and fragile as to peel off very often, thereby resulting in a lowering of thermal efficiency of the furnace.
The main object of this invention is to provide an improved water-cooled panel for arc furnaces which eliminates the above described disadvantages of the prior art and requires a smaller flow of water coolant circulating therethrough, whereby the thermal efficiency of the furnace can be increased.